add help docs and ?

docs/nodes/Angle Measure.md

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+# Angle Measure
+
+Measure the included angle between two draggable line segments over a DATA_FIELD or IMAGE. Drag either endpoint to change that arm, drag the middle joint to move the whole widget, and drag the angle label to reposition it.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| input | ANNOTATION_SOURCE (DATA_FIELD or IMAGE) | Yes | Background image or field to annotate |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| output | ANNOTATION_SOURCE | Input with the angle overlay attached |
+| measurements | RECORD_TABLE | Angle in degrees, arm lengths, and arm/vertex coordinates |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| color | STRING (color picker) | #ff9800 | Overlay color for the angle arms and arc |
+| stroke_width | FLOAT | 1.35 | Line thickness in display pixels (0.35–6.0) |
+
+## Limitations
+
+- Coordinates are stored as fractions of the image dimensions; physical units depend on the input field's calibration.
+- Angle measurement is the included angle at the vertex, always in [0°, 180°].